The invention relates to a method of recognizing a pattern in a field having a multi-valent amplitude by association with a reference mask which is composed of logic high and logic low units.
The invention also relates to a device for performing such a method.
A method and device of the kind set forth are known from the German Offenlegungsschrift DE-OS 32.10.814 corresponding to U.S. Pat. No. 4,491,962 in versions which relate to the recognition of patterns in video images composed of pixels of different grey values.
The known method converts the multi-valent video image into several images with binary units, each image being converted on the basis of a different discrimination threshold. Parts of several of these images, which parts correspond to one another as regards location, are compared with a binary reference mask which represents the desired pattern. The degree of correspondence between a part of an image considered and the reference mask is then determined by the number of units in the relevant part which have the same logic value as the units of the reference mask which correspond thereto as regards location. This degree of correspondence is a discrimination threshold dependent quantity.
As the most suitable discrimination threshold for the thresholding of the video image in order to detect and localize the desired pattern, the discrimination threshold is used for which the cumulative degree of correspondence between each of the relevant parts of the thresholded video image on the one hand and the reference mask on the other hand is maximum.
In accordance with the known method, the transformation of the video image by thresholding must be performed with all feasible thresholds before a maximum degree of correspondence can be found wherefrom the presence or absence of the desired pattern can be deduced. When thresholding with the various thresholds is successively performed and when a customary number of thresholds is used (for example, 256 different thresholds), the overall thresholding operation is time consuming. When thresholding of the input image is simultaneously performed for all thresholds, expensive facilities will be required for the parallel thresholding of 256 video images and for keeping the transforms ready for subsequent operations.